Conventionally, a typical method for forming an oxetane ring includes: a method of coupling a hydroxy group with a methyl group, adjacent to the hydroxy group, having a leaving group; and a method of adding a double-bond compound to a carbonyl compound (see Non-patent Literature 1). Other examples of the method for forming an oxetane ring include: a method of reacting an aldehyde with a cyanide (see Non-Patent Literatures 2 and 3); a method of reacting a haloalkyl ketone with a cyanide (see Non-Patent Literature 4); and a method of refluxing diol mesylate or diol tosylate in a base (see Patent Literature 1).